MADRID—Spain’s Constitutional Court on Wednesday struck down a resolution by the parliament of the wealthy Catalonia region to launch a process of secession from Spain.

The 11 court justices voted unanimously to annul the Nov. 9 resolution, which set out a plan for “democratic disconnection” from Spain. The ruling said the Catalan parliament’s action had no basis in Spanish law and the independence resolution “infringes the constitutional rules that say national sovereignty resides with the Spanish people.”